SILICON DIOXIDE SEMICONDUCTOR PRODUCT CONTAINING BORON TRIOXIDE AND PHOSPHORUS PENTOXIDE DOPANTS

摘要

1432949 Semi-conductor devices PLESSEY CO Ltd 2 Aug 1973 [25 Aug 1972] 39669/72 Heading H1K The ratio of boron to phosphorus in a silicon dioxide layer containing both is chosen so that the layer may be etched at the same rate as, e.g. undoped silicon dioxide. The doped layer contains 10-25 (preferably 15) wt. per cent boron trioxide and 10-30 (preferably 20) wt. per cent phosphorus pentoxide, the balance being silica. The layer may be formed by the thermal interaction of silane, phosphine, diborane, an oxygen. A typical etchant comprises 4 parts saturated ammonium fluoride solution and 1 part hydrofluoric acid. The use of the doped silica is illustrated in the manufacture of an IGFET. A silicon substrate 4 has an area of a thermal oxide layer 2 replaced by a thermal oxide film 8 and this is covered by polycrystalline silicon 10. Diffusion apertures for source and drain are etched through layers 8 and 10, and diffusion is effected. At the same time as or subsequent to the formation of the source and drain regions (not shown) an oxide layer 17 is formed. The boron and phosphorus doped silica layer 18 is then deposited and the structure heated to smooth the contours of this layer. Source and drain contact apertures are then etched through layers 18 and 17 and a further contour smoothing may be effected. Aluminium (not shown) is then deposited overall, and removed where not required. A protective silica layer (not shown) may be applied overall.